Wall effect on single bubble rising in a Hele-Shaw cell

Single air bubble rising near vertical wall in a Hele-Shaw cell was investigated experimentally. Bubbles with a large range of size from 4.46 mm to 21.68 mm were generated. A vertical wall was introduced in the cell, and the initial distance between the wall and the bubble releasing position was varied systematically to study the wall effect on the rising dynamics. Rising trajectory, bubble morphology, and rising characteristics were analyzed. Bubble will migrates away from the wall, and the trajectory transits from rectilinear path to zigzag. Two mechanisms of zigzag were revealed as "rigid zigzag" for the small bubble and "contracting zigzag" for the large bubble. It is always easier to zigzag for a more rounded bubble, and migration is always stronger with a smaller normalized initial distance.